(1) Field of the invention
The present invention is related to a variable speed transmission used in the automobile, particularly a device to improve the transmission efficiency in electric cars.
(2) Description of the prior art
The research and development on electric cars were started in 1830. As compared to the engine automobiles, the electric cars have the advantages of energy conservation, minimum environmental pollution, low noise and stable in operation. On the other hand, the battery in electric car weighs as high as a few hundred kilograms, and the energy density is only 40 to 45 Watt per hour, the disadvantages of insufficient horsepower, low operating efficiency, short distance in continuous operation as well as battery recharging existed in electric cars. After the invention of the automatic ignition in combustion engine, the automobiles with combustion engines have dominated the market in the twentieth century. Due to the energy crisis and the pollution caused by the fuel engine, the world is paying more attention and reconsidering the advantages of electric cars, regardless of their disadvantages.
In order to reach the stages of practical application, the electric cars have to overcome the drawbacks of insufficient power, low operating efficiency and short continuous operating distance. One way to overcome the above obstacle is to develop highly efficient batteries, and another more direct way is to decrease the weight of the variable speed transmission and increase the transmission efficiency. So far there is no break through in the development of high grade batteries, conventional lead acid battery has a low energy density, the recently developed batteries have their disadvantages and are not practical yet. For instance, although the sodium sulfate batteries have a higher energy density, they have to be operated under a high temperature environment of 260 C. and they are explosive under an accidental impact, the zinc type batteries require additional accessories such as compressor, pump, separator, purified storage tank, etc.; and they are difficult to be recharged. The Lithium battery operating under high temperature takes a long time to recharge and the battery life is short. The general Nickel Cadmium battery is expensive and its energy density is about the same as the lead acid battery. Although the Silver Zinc battery has a better energy density, its price is very expensive and can be recharged about 100 times only. Therefore, based on the current manufacturing technologies, development on the high efficiency, light-weight variable speed transmission is one of the best way to improve the efficiency of electric cars.
The operating principle and structure of the electric car are different from the fuel engine driven automobile. The electric car uses the dc motor to replace the engine, the battery to substitute the fuel, main control circuit to replace the function of the carburetor; among them the battery is used to power the dc motor, the Silicon-Controlled Rectifier (SCR) in the main control circuit is used to adjust the terminal voltage of the dc motor so as to control the speed of the electric car. Although the main control circuit can control the revolution and the speed of the dc motor, the horse-power cannot be adjusted and controlled based on the operating condition, this is causing a low start up, slow down in speed and unbalanced in power consumption during operation. The above drawbacks can be compensated and improved by installing a variable speed transmission drive to provide a different rotating speed between the motor shaft and the drive shaft, this device can give a higher torque and horsepower during the low speed operation, it can also reduce the number of revolutions of the motor at high speed operation. This installation can therefore improve the battery efficiency, the low start up torque, slow speed and unbalanced electric power consumption in the operation of the electric cars.
The conventional variable speed transmission is classified into three types: the manual transmission, the automatic transmission and the continuously variable transmission. The manual transmission changes the ratio between the rotating speeds of the engine and the wheels by the use of gears, it has the highest efficiency in transmissions. In the operation of the automobile with Manual transmission, the driver has to apply and release the clutch as well as shift the lever based on the speed of operation, this is causing an emotional and physical burden to the driver, especially during the traffic jammed condition.
Drivers in automobiles with Automatic transmissions do not have to worry about the clutch and the shift lever. The car is easy to operate and thus reduce the risk of accident. The automatic transmissions use fluid power and its fluid torque converter has a slip phenomenon in the system, the efficiency is not ideal and the lagging causes the automobiles with Automatic transmission consume more power, slow down in accelerating and decelerating as well as the drawback of frequent braking.
Continuous variable transmission consists of a pulley belt and a pair of grooved wheels, the pulley and its wheels generate a high torque of transmission, the centripetal force generated from the pulley induced a highly compressed force on the triangular shaped pulley, therefore the pulley has to have a certain degree of thickness to avoid breaking from the centripetal force. The increase of thickness in the pulley will relatively increase its centrifugal force so as to cause a higher surface tension of the pulley. Besides the increase of thickness in the pulley also cause an increase in the diameters of the wheels. In addition, the belt is traveling through the grooved wheels and is causing more friction, this is a negative impact in the overall efficiency and the operational life of the continuous variable transmission.
The above mentioned conventional transmissions cause complicated structures, heavy weight, large physical size and low transmission efficiency. If installed in the electric cars, they would certainly impose a heavy load on the batteries, and this is the reason electric cars use speed reducer instead of the variable transmissions.